Pavlos is King Charles III's second cousin once removed, but Queen Elizabeth II's third cousin once removed only. If I am not mistaken, his degree of kinship to the late Queen Elizabeth II is the same as Crown Prince Frederik's.
I have just heard on Sky News that, contrary to what the Royal.uk site suggested, "foreign royals and Knights of the Garter" will be present at the committal service. It is not clear yet if all European monarchs or only part of them will be at both services in London and Windsor, but I look forward to finding out tomorrow.
Unfortunately I won't be able to follow the committal service live, because I will be working at that time (it is not a holiday for us!), but I will try to catch up later.